The present invention relates to gas turbine engine casings, particularly gas turbine engine fan casings, more particularly to an improved blade containment assembly for use within or forming a part of the gas turbine engine casing.
Turbofan gas turbine engines for powering aircraft conventionally comprise a core engine, which drives a fan. The fan comprises a number of radially extending fan blades mounted on a fan rotor which is enclosed by a generally cylindrical, or frustoconical, fan casing. The core engine comprises one or more turbines, each one of which comprises a number of radially extending turbine blades enclosed by a cylindrical, or frustoconical, casing.
There is a remote possibility that with such engines that part, or all, of a fan blade, or a turbine blade, could become detached from the remainder of the fan or turbine. In the case of a fan blade becoming detached this may occur as the result of, for example, the turbofan gas turbine engine ingesting a bird or other foreign object.
The use of containment rings for turbofan gas turbine engine casings is well known. It is known to provide generally cylindrical, or frustoconical, relatively thick metallic containment rings. It is also known to provide generally cylindrical, or frustoconical, locally thickened, isogrid, metallic containment rings. Furthermore it is known to provide strong fibrous material wound around relatively thin metallic casings or around the above mentioned containment casings. In the event that a blade becomes detached it passes through the casing and is contained by the fibrous material.
In the event that a blade becomes detached, the metal casing is subjected to two significant impacts. The first impact occurs generally in the plane of the rotor blade assembly as a result of the release of the radially outer portion of the rotor blade. The second impact occurs downstream of the plane of the rotor blade assembly as a result of the radially inner portion of the rotor blade being projected in a downstream direction by the following rotor blade.
Accordingly the present invention seeks to provide a novel gas turbine engine casing which reduces damage and/or penetration of the gas turbine engine casing downstream of the plane of the rotor blade assembly.
Accordingly the present invention provides a gas turbine engine rotor blade containment assembly comprising a generally cylindrical, or frustoconical, containment casing, the containment casing having an upstream portion, a blade containment portion and a downstream portion, the blade containment portion being downstream of the upstream portion and upstream of the downstream portion, the downstream portion having impact protection means located on its inner surface to protect the downstream portion.
The impact protection means may comprise at least one rib extending circumferentially and radially inwardly from the downstream portion of the containment casing. The impact protection means may comprise a plurality of ribs extending circumferentially and radially inwardly from the downstream portion of the containment casing and the ribs being axially spaced.
The impact protection means may comprise a stiff and lightweight material arranged within and abutting the downstream portion of the containment casing. The stiff and lightweight material may be bonded to the downstream portion of the containment casing.
The stiff and lightweight material may abut the downstream portion of the containment casing axially between the ribs.
The impact protection means may comprise a liner arranged within and abutting the downstream portion of the containment casing. The liner may comprise a plurality of ribs extending radially inwardly, the ribs extending circumferentially and/or axially. The liner may comprise a stiff and lightweight material between the ribs. The liner may be bonded to the downstream portion of the containment casing.
The stiff and lightweight material may comprise honeycomb. The stiff and lightweight material may comprise a metal honeycomb and a metal plate abutting the inner surface of the metal honeycomb. The honeycomb may have a dimension of about 3 mm between the parallel walls of the honeycomb and the walls of the honeycomb may have a thickness of about 0.025 mm to 0.1 mm.
The containment portion may have ribs and/or flanges. The thickness of the blade containment portion may be greater than the thickness of the upstream portion and may be greater than the thickness of the downstream portion. One or more continuous layers of a strong fibrous material may be wound around the containment casing.
The containment casing may comprise any suitable metal or metal alloy. Preferably the metal containment casing comprises a steel alloy, aluminium, an aluminium alloy, magnesium, a magnesium alloy, titanium, a titanium alloy, nickel or a nickel alloy.
An acoustic lining may be provided within the containment casing.
The blade containment portion may have a radially inwardly and axially upstream extending flange, the flange being arranged at the upstream end of the blade containment portion.
The containment casing may be a fan containment casing, a compressor containment casing or a turbine containment casing.